Today's communication systems are approaching the maximum threshold that can be used in terms of bandwidth size or data throughput. To further improve channel capacity, it is necessary to resort to higher frequency electromagnetic wave bands, which makes the millimeter-wave communication an important development direction for future mobile communication, because its large frequency band will bring more ideal channel capacity, which will make the transmission of large amounts of data feasible, and many communication specification, such as fifth generation mobile communication, vehicle detection radar, etc. to be developed.
However, the millimeter wave will withstand the high air loss effect at high frequencies (above 30 GHz), so that the transmission signal will have a serious loss in a short distance, and the ideal signal noise ratio cannot be obtained at the receiving end (Signal to noise ratio), here, the millimeter wave communication system needs to use beamforming technology (Beamforming) to obtain sufficient antenna gain to resist large air loss in high frequency, thereby effectively improving the signal noise at the receiving end.
However, beamforming technology requires accurate channel information to synthesize an ideal precoder. With accurate channel information, the base station can perform transmission power allocation and determine which path is preferably for data transmission. Therefore, the millimeter wave channel estimation method is an indispensable important technology.
The millimeter wave communication system uses a massive multiple input multiple output (MIMO) system, and a large number of tiny antennas are deployed at the transmitting end and the receiving end. In the existing communication system, each antenna is equipped with a set of independent RF chains and digital/analog (D/A) converter for fully digital beamforming. However, it is not practical to deploy the same hardware architecture on the millimeter wave communication system. A large number of RF chains and D/A converters will greatly increase the hardware cost of the system. Therefore, the millimeter wave communication system adopts hybrid beamforming technology, the number of RF chains and D/A converters in this architecture is much smaller than the number of antennas, and each antenna is equipped with a phase shifter to reduce costs with this hybrid hardware architecture while approaching the fully digital beamforming technology in performance. The hybrid system is quite different from the previous fully digital beamforming architecture, and thus different method for processing the channel estimation is utilized.
Moreover, the dimensions of the millimeter-wave channel matrix are much larger than in the previous communication systems, and the distribution of the channel paths is rather sparse due to the high air loss characteristics of the high-frequency electromagnetic waves, and thus objects that actually reflect and scatter the path of the channels are relatively rare. These characteristics make the channel estimation method in the existing communication system no longer meet requirements for the actual application. However, the existing scheme is not ideal in the training overhead and feedback numbers of channel estimation information, and therefore the process of estimating the channel will consume a certain amount of resources.